Flotation process of clarifying regenerating baths



Patented Mar. 1, 1949 UNITED STATES PATENT oFri'ce rtorarron rnocass orctnmryme anennnm'rme BATHS Joseph. L. Costa, Woonsocket, and WilliamHarlow Kaliler, Saylesville, It. I..- asslgnors, 'liy mesne assignments.to Woonsocket Rayon, Inc., a corporation of Delaware No Drawing.Application May 19, 1943,

Serial No. 487,840

6 Claims. 1

The present invention relates to improvements in the flotation processof clarifying regenerating baths used in the preparation of cellulosicarticles of artificial origin. More specifically it has to do withcarrying out of the process in the presence of a betaine in theregenerating bath.

The primary object of this invention is to provide a composition ofregenerating medium which will allow an economical and eflicientapplication of the flotation process and which will be entirely freefrom deleterious eifects upon the extrusion step. The application ofthis invention to the viscose process will be described in detail in thefollowing specification, but it will be'understood that the scope of theinvention is intended to embrace any process of regener'atlngcellulosicsolutions in which the regenerating medium, in general a liquid bath,becomes fouled with impurities or by-products inherent to the extrusionstep, such as, for example, the cuprammonium process.

In accordance with the applicants invention the process of purifying theregenerating bath by flotation, which has been the subject of severalUnited States Letters Patents, including Nos. 2,105,684 and 2,153,449,is carried out in the presence of an acid stable frothing agent, whichcompound is characterized by the following general formula:

resulting the loss of the ionizable H from concentrations particularlythose containing acid.

The importance of this property will be shown resulting from the loss ofthe ionizable H'- from the sulfonic acid group in consequence of theneutralization of the latter upon the nitrogen a om.

Applicants have found that the presence of minute quantities ofcompounds of the above structure makes possible the production of acopious froth by the use of flotation machinery of conventionaldesigneven when dealing with regenerating baths of the usual highelectrolyte This result is not obtainable by the use of the usualflotation reagents in the presence of high electrolyte and acidconcentrations. Moreover it has been found that such substances areexcellent collectors of the sulfur and other impurities usually found inprecipitating baths so that the flotation process is very emcientwithout the further addition of substances which might be deleterious tothe extrusion step.

A further advantage exhibited by the compounds of the structure setforth above is their freedom from forming precipitates with the heavymetals which are usually present in regenerating baths,

for example, zinc and lead. An important source of loss of compoundsused in minute quantities is thus prevented.

A still further advantage of such compounds is their lack of pronouncedionogenic tendencies.

below: The efflciency of the flotation method as a whole for theclarification of rayon regenerating baths depends in no small part uponthe prevention of accumulation of solid impurities at 86 their point ofinception, i. e., at, and even in the the carboxyl group in consequenceof the neutralization ofthe latter upon the nitrogen atom. Likewise, byresidue of a sulfonic acid group is meant the configuration V spinneretorifices themselves.' Since the formation of solid impuritiesundoubtedly takes place at or .near the boundary between the stronglyalkaline spinning solution and the highly acid regenerating bath, it isobvious that a surface active agent substantially neutral in characterwill have the best likelihood of being present in the critical zone ofprecipitation of such impurities. As a result of the presence ofcompounds of the structure disclosed above the precipitated solidvParticles of impurities are prevented from agglomerating or adhering tothe spinneret surfaces and are rendered hydrophobic in character, so asto be readily removed by the flotation process.- In other words thespecial virtue'oi these compounds is that they are strongly polar. butwith little-or no tendency to ionize.

- In this connection it should be pointed out that many of the surfaceactive agents heretofore r. 55 employed for attaining the abovementioned ends,

. aceaaea asexemplified by the cation active compounds.

have a marked afllnity for cellulose, which property results in a highrate of exhaustion by the continuous production of a fresh cellulosesur- '1. In the froth flotation process of clarifying We'claim:

face as the extrusion process is carried out over 5 which baths arefouled by impurities incident to I. (a) In a commercial operation aregeneratby cit- 2 P. P. M. in a single pass.

ing bath containing approximately sulfuric acid and sodiumsulfate byweight was treated continuously with an amount of C-cetyl trimethylbetaine that would give approximately 0.00003% of the bath beingcirculated from the storage and heating tanks over the spinning framesand through a flotation machine of conventional design before returningto the, storage tanks. It is estimated that under such conditions aconcentration of the C-cetyl trimethyl betaine was maintained at a levelof approximately above the ratio at which it was addedowing m/theregeneration step, the step of floating said impurities out of the bathin a froth formed in the presence 'of a betaine of the following generalformula:

I Rr-N-Jh il 2. In the froth flotation process of clarifying acidregenerating baths for repeated use in the preparation of cellulosicarticles from viscose, which baths are fouled by impurities incident toto the incomplete removal of the frothing agent in the flotation step.Under such con-- ditions the amount of suspended impurities in thespinning bath was reduced from 18 P. P. M. to 5 P. P. M. by a singlepassthrough the flotation'machine, the concentration of suspended impuritiesbeing determined- 'by turbidimetric records which previously ha beencalibrated gravimetrically.

(b) In a continuation of the operation described above the addition ofthe C-cetyl trimethyl betaine was doubledwith the fol-' lowing results:The average suspended matter was reduced from 14 P. P. M. to 2 P. P. M.during a single pass through the flotatioh machine.

(c) In a further continuation of the operations the addition of the'C-cetyl trimethyl betaine was trebled over that used in I (a), i. e.brought to approximately 0.0001%, with the following results: Thesuspended impurities were reduced from 13 P. P. M. to However, theamount of froth was excessive under these conditions resulting indiiflcult manipulation of the flotation machine and the loss ofconsiderable quantity of the spinning bath. It is concluded from theabove tests that the optimum amount of this frothing agent in a bathofapproximately the composition cited would be near to that mentioned inExample I (b).

II. In a similar manner the compound C-myristyl trimethyl betaine wastested at varying rates from 0.00003% to 0.00008%. The results in thiscase were substantially the same except that the optimum concentrationwas found to lie slightly higher than that of the C- cetyl betaineabove. I

the scope of the the regeneration step, the step of floating said 26'impurities out of the bath in a froth formed in the presence of abetaine of the era] formula: a

following gen- Rr/-N B| I i--X wherein Nis a nitrogen atom, R1 is analkyl group of from 3 to 20 carbon atoms, Ra, R: and R4 are 36 alkylgroups at least one of which must contain from 8 to 20 carbon atoms inthe event that R1 contains less than 5 carbon atoms, and X representsthe residue of a carboxyl group.

3. The process as described in claim 2 in which I The followingreferences are of record inthe JOSEPH L. COSTA. WILLIAM HARLOW KAHLER.

REFERENCES CITED 5 die of this patent:

UNITED STATES PATENTS Number Lontz.. Dec. 21 1943

